1. Field of the Invention.
This invention relates to an improved electromagnetic interference (EMI)/radio frequency interference (RFI) shield. This shield is placed in front of visual display terminal screens.
2. Prior Activities in the Field.
There is an ever increasing need for EMI/RFI shields for visual display terminal screens. These screens are commonly cathode ray tubes but also can be flat panel devices. The need for these filters arises from several fronts. For one, there are health concerns regarding operators being exposed to EMI and RFI radiation emanating from the display devices. For another, there is concern over interference from one device to another from the EMI/RFI radiation they each emit. Another growing concern is the need for security within computers and other systems which employ visual display terminal screens and the recognition that computers and the like can be probed through the screens.
While it is possible to shield most areas of these devices by enclosing them in a conductive shield such as a wire mesh shield or metal box, shielding the display surface itself where visual clarity is important can be more difficult. Heretofore, wire mesh based shields have been proposed for the display surfaces. While these generally work acceptably with monochrome systems, with color displays, which employ a dot matrix style of display, wire mesh can seriously degrade signal patterns by creating moire patterns. This interference can also lead to color shifts.
Glass panel shields with transparent metal coatings have been proposed as well. These materials have a transparent substrate with a layer of metal on one surface. They have numerous failings. For one, the panels are extremely costly and difficult to work with because of their glass construction. For another, such panels tend to be thick and heavy.
Representative disclosures relative to EMI/RFI shielding and to the use of shielding in security environments includes:
U.S. Pat. 4,412,255 issued 25 Oct. 1983 to Bruce E. Kuhlman and Marc A. Kamerling.
As will be apparent from the foregoing, there is a well recognized need for a high efficiency EMI/RFI shield for use with visual display terminals. The prior art has not supplied such a shield and it is the object of this invention to do so.